Articles of filled synthetic polymeric materials and glass bead filler therefore

ABSTRACT

In or for a polymeric article incorporating a synthetic polymer and a filler material, which filler material includes glass beads bearing coatings of at least one coating agent in a total coating amount not exceeding 1% and preferably between 0.02% and 0.2%, by weight based on the weight of uncoated beads, which coatings limit adhesion between the glass beads and the synthetic polymer and confer an increased impact resistance on the article as compared with an article which includes uncoated glass beads as filler material but is otherwise identical.

This is a division of application Ser. No. 07/041,667 filed Apr., 20th,1987, which is a continuation of application Ser. No. 06/754,452 filedJuly 11th, 1985.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to synthetic polymeric articlesincorporating glass beads as filler material, and to glass bead fillermaterials for use in the preparation of such articles.

2. Discussion of the Art

It is well known to fill synthetic polymeric materials with glass beads.Depending on: (a) the specifications of the beads, (b) the treatment, ifany, to which the beads are subjected before being mixed with thesynthetic polymer or synthetic polymer precursor, and (c) thebeads/synthetic polymer quantity ratio, the presence of the filler canfacilitate working of the compounded material and can, in variousrespects, enhance some mechanical properties of articles formed from thematerial. Spherical glass beads, for example, are capable of improvingstress distribution within moulded articles as well as facilitating themoulding process itself. All these facts are well known (see e.g.,"Glass microspheres: bubbles and beads as plastics additives" by DarrelL. Muck and James R. Ritter, "Plastics Compounding": January/February1979, page 12.

It is recognised in the art that while glass beads, used as a syntheticpolymer filler, can result in some improvement in various mechanicalstrength properties of articles formed from the synthetic polymericmaterial, such as their flexibility and tensile strength, the presenceof the beads often has an adverse effect on the impact strength of thearticles. This is particularly the case when using solid, as distinctfrom hollow, glass beads.

SUMMARY OF THE INVENTION

The present invention enables this adverse effect on impact strength tobe avoided or reduced.

The invention is based on the discovery that a degree ofshock-resistance can be given to articles moulded from the filledsynthetic polymer by suitably surface coating the glass beads used asfiller.

According to the present invention, there is provided a syntheticpolymeric article incorporating glass beads as filler material,characterised in that the glass bead filler material comprises beadsbearing coatings of at least one coating agent in a total coating amountnot exceeding 1% by weight of the uncoated beads, which coatings limitadhesion between the glass and the synthetic polymeric material andconfer an increased impact resistance on the article as compared with anarticle which includes uncoated glass beads as filler but is otherwiseidentical.

The invention also includes mouldable or otherwise formable syntheticpolymeric material incorporating glass beads as a filler, characterisedin that the beads bear coatings of at least one coating agent in a totalcoating amount not exceeding 1% by weight of the uncoated beads, whichcoatings limit adhesion between the glass and the synthetic polymericmaterial and confer an increased impact resistance on articles whenformed from such filled synthetic polymeric material as compared with anarticle which includes uncoated glass beads as filler but is otherwiseidentical.

It is surprising that a significant improvement in impact strength canbe achieved merely by applying a rather thin surface coating to thebeads. As will hereafter be exemplified it has been found that impactstrength can easily be increased by over 20% simply by appropriatelycoating the beads.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a graph comparing the impact resistance of sheets ofepoxy-amine resin filled with solid glass beads as a function of beadconcentration for styrene-butadiene coated beads (curve 1) and uncoatedbeads (curve 2).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is not necessary to form very thick coatings on the glass beads. Inpreferred embodiments of the invention, said coating amount is between0.02% and 0.2% by weight of the uncoated beads. We have found that theuse of such quantities of coating agent is not only beneficial forreasons of economy, but also that it tends to promote an increase inimpact strength. Preferably, said coating amount is not more than 0.1%by weight of the uncoated beads. Good results have been obtained, forexample, when using polymeric coating material in an amount of about 0.2to 1.0 g per kg of glass beads having a specific surface of 0.3 m² /cm³.

Various methods are available for testing the impact strength of aspecimen product. One particularly appropriate test for materials of thekind under consideration is ASTM Test D 2794 which determines the effectof the impact of a dart. Another is the generally similar Gardner test,and a third is the Charpy test. Impact resistance values given in thisspecification are values determined by one of these tests.

Adhesion between the glass and the synthetic polymeric material may forexample, be limited by using a coating agent which bonds well to glassbut has a limited adherence to synthetic polymeric material, or by usinga coating agent which bonds well to synthetic polymeric materials, butless well to glass.

Various coating agents having a limited adherence to synthetic polymericmaterials may be used in the performance of this invention. Among suchcoating agents are of silicones, silanes-especially silicon-functionalsilanes, and oleophobic fluorocarbon compounds. It is preferred thatsaid coatings comprise a silane and/or a fluorocarbon compound. Suchmaterials can be arranged to bond well to glass, while having a limitedcapacity to adhere to synthetic polymeric materials. This has theadvantage of forming a coating which confers the required propertieswhile at the same time being resistant to removal from the beads duringhandling prior to incorporation in a synthetic polymeric material. Verygood results have been achieved using a silane which is an alkyl-silaneor an aryl-silane, as is preferred, and it is especially preferred touse methyl-silane or phenyl-silane. In embodiments of the inventionmaking use of a fluorocarbon compound coating agent, it has been foundpreferable to use an anionic fluorocarbon compound, and in particular afluoro-alkyl-sulphonate, since this gives good results.

In some preferred embodiments of the invention, said coatings comprise asynthetic polymeric material having shock-absorbing properties. Ingeneral it is found that such coatings adhere less well to glass beads,and so are more apt to be removed by careless handling prior toincorporation in synthetic polymeric material as filler, but it has beenfound that when so incorporated beads coated in this way tend to confera greater improvement in impact strength on synthetic polymericarticles.

Suitable synthetic polymeric materials for coating beads for use in themanufacture of products according to this invention include elastomersproperly so called and other polymers incorporating chain units orsegments which undergo straightening or change in orientation understress, with consequent energy-absorption. In view of the use to whichthe coated beads are put, such coating material must normally be capableof energy absorption at ordinary room temperature which implies a lowglass transition (T_(g)) temperature. Such an energy-absorbing syntheticpolymeric material is preferably a material for which the glasstransition temperature (T_(g)), determined by differential scanningcalorimetry, is lower than 15° C.

Prior to coating the beads with a synthetic polymeric material, they canbe treated with a coupling agent to promote required adhesion of thepolymer coating to the beads, and it is preferred that the adhesion ofsaid polymeric coatings to the glass beads is influenced by the presenceof a coupling agent comprising a silane. It is well known to employcoupling agents for improving the interfacial bond between a mouldablesynthetic polymeric matrix and glass beads which are incoporated thereinas filler. The coupling agents used for this purpose are customarilyselected to achieve as strong an interfacial bond as possible because astrong adhesion benefits various strength properties, for example, theflexural strength and modulus of the composite material. However, whenselecting a coupling agent for influencing the interfacial bond betweenglass beads and polymeric surface coatings prior to incorporation of thecoated beads into the synthetic polymeric matrix material to produce acomposite according to the present invention, other considerationsapply. It has been found that while it is important for the bead coatingmaterial to adhere to the beads, any coupling agent used should not beselected with the object of making the interfacial bond as strong aspossible because a very high strength is helpful to the main purpose forwhich the beads are coated. A very strong adhesion can prevent fullexploitation of the ability of the coatings to improve the impactstrength of a formed article. If the structure of the polymeric, beadcoating material comprises segments or groups of differentenergy-absorbing potentials the coupling agent can be selected to anchorthe polymer via its rigid or less deformable structural segments orunits, leaving the other parts of the molecular structure free toundergo reorientation under stress. The strength of the interfacial bondactually achieved can be controlled by mixing one coupling compound withanother to form a composite coupling agent, and it is especiallypreferred that said coupling agent comprises a mixture of differentsilanes and forms an interfacial bond of a strength intermediate thatattainable by either component if used alone.

A particularly suitable energy-absorbing coating is one formed of astyrene-butadiene copolymer such as that commercially available fromPolysar Europe S.A. of Zwijndrecht, Belgium and designated X818. In astyrene-butadiene copolymer, the styrene units have a T_(g) of 60°-70°C., but the T_(g) of the butadiene units, which are responsible for therequired energy-absorbing property of the material, is below 15° C.Another useful bead coating material is copoly(NH₂-butadieneacrylonitrile-NH₂). Also, copoly(butylacrylate-epoxyacrylate)can be used. However there are reservations in recommending the lattermaterial because acrylic polymers have poor resistance to temperatureswhich are normally (depending on the composition of the syntheticpolymeric matrix material) employed in moulding operations.

The bead coatings can be formed by application of the coating materialas a solution or as a latex (aqueous suspension). It suffices for thebeads to be immersed in the coating material, drained and dried.

Glass beads of any of a wide range of specification can be selected foruse in carrying out the present invention. The size and form of thebeads are of influence, as known per se in relation to fillers, on theproperties of articles formed from the composite material. In the mostimportant embodiments of the invention the beads are solid. Solid beadsare particularly preferred as filler for thermoplastic resins because oftheir greater crush resistance. The invention enables the particularbenefits of solid glass beads as a filler, including their inherentstrength which is an advantage for the forming operation as well as forthe properties of the moulded product. to be combined with that of ahigher product impact strength than that which would normally beattainable with such beads. Normally, the lowering of impact strengthresulting from the use of glass beads as synthetic polymer filler isparticularly marked if the beads are solid.

The glass beads used in carrying out the invention are preferablyspherical in order to realise the benefits for the flow properties ofthe filled synthetic polymer, and in order to promote even stressdistribution within articles formed therefrom, which is known to beassociated with a filler of that form.

The size of the beads is a factor which influences the properties of amaterial according to the present invention in the same way as in knownmaterials using uncoated glass beads as the filler. It is generallyappropriate to use beads less than 500 μm in diameter and for mostpurposes it is recommended to use beads of a much smaller maximumdiameter, for example, beads of diameters less than 200 μm.

The beads preferably have a narrow size range distribution (andtherefore a low apparent bulk density) because they can then be betterdistributed in the formable matrix material so that shock is transmittedthrough the resin and not directly from bead to bead. Preferably theirapparent bulky density is from 1.5 to 1.55. If the beads are confined toa narrow size range, the viscosity of the formable materialincorporating the beads increases steeply with increase in thebead/matrix quantity ratio and this must be taken into account whenselecting this ratio for a particular composite material.

In certain articles and materials according to the invention, the glassbeads have a granulometry such that 90% of the beads have a diametersmaller than a length x and 10% of the beads have a diameter smallerthan a length y, the values of x and y being such that x - y is greaterthan 45 μm but smaller than 65 μm.

The beads are preferably made of a soda-lime glass (A glass).

An article or formable material according to the invention canincorporate filler comprising the coated glass beads and at least oneother kind of discrete material. For example the filler may comprise inaddition to the coated glass beads, a finely divided material whichmodifies the bulk density of the filler. Such a finely divided materialcan for example serve to reduce the extent to which the viscosity of thesynthetic polymer/bead mixture increases with increase in thebead/synthetic polymer quantity ratio. Such finely divided material can,with advantage, be a hydrophobic, inorganic substance which issubstantially chemically inert with respect to the beads and has aspecific surface of at least 50 m² /g. Compositions incorporating such acomposite filler and wherein the said hydrophobic finely dividedcomponent is present in an amount not more than 5% by weight of theglass beads, are described and claimed in our copending United KingdomPatent Application No. 83 31 375, filed Nov. 24, 1983. Particularlyrecommended materials for the finely divided hydrophobic component ofthe filler are the silicas commercially available from Degussa(Frankfurt) under their Trade Mark AEROSIL and from Cabot Corporation(Tuscola, Ill.) under their Trade Mark CAB-O-SIL.

The selection of the bead coating material for a particular kind ofcomposite should take account of the composition of the mouldable matrixmaterial into which the coated glass beads are to be incorporated. Thestrength of the interfacial bond between the bead coatings and thematrix is a factor which can influence the tensile and bending strengthsof the product as well as its impact resistance. A low adhesion which isdesirable for promoting impact strength can adversely affect bendingstrength and modulus, and if all of these factors are important for agiven product, the selected combination of matrix material and adhesionlimiting bead coating material should represent an appropriatecompromise. The strength of the adhesion is dependent on the surfacetension difference between the bead coatings and the matrix.

The synthetic polymeric matrix material can be a thermoplastic, forexample, a polyamide or polystyrene, or a thermosetting resin, forexample, an epoxy or polyester resin. Application of the invention inthe manufacture of mouldable glass/polyamide composites and glass/epoxyresin composites and of articles formed from such composites isconsidered to be of particular interest, both for technical andcommercial reasons.

The mixing of the coated beads with the matrix material is easier ifthis material is in liquid state as is the case, for example, when usinga two-component epoxy resin composition.

The quantity ratio of coated beads to synthetic polymeric matrixmaterial is a factor of importance in various respects. The benefits forimpact resistance increase, within a certain range, with the proportionof coated beads in the composite material. Above a certain concentrationof the beads, the impact resistance begins to decrease because of directbead to bead contacts.

The influence of bead concentration on impact resistance is representedby the accompanying FIGURE which is a graph in which impact resistancevalues appear on the ordinate and bead concentrations (in parts byweight of beads per 100 parts by weight of synthetic polymeric matrixmaterial) on the abscissa. The two curves 1 and 2 both relate toarticles formed from composites comprising an epoxy-amine resin mixtureand solid glass beads as the synthetic polymer filler, the solid glassbeads and the matrix material being that used in Example 1 givenhereafter. Curve 1 relates to articles in which the glass bead werecoated as in the Example 1. Curve 2 relates to articles in which theglass beads were uncoated. It will be seen that the impact resistance isgreatly improved by the presence of the bead coatings. But for both thecoated filler and the uncoated filler categories of article there is amaximum filler proportion above which the impact strength begins todecrease.

In the case of spherical beads, their presence facilitates the shapingof the composite, by injection or extrusion moulding or otherwise, andfrom all of these standpoints, as well as for cost reasons, a highproportion of beads is an advantage, but the proportion which can beused in any gven product is limited by other considerations such as theinfluence of the beads on the viscosity of the composite material. Whenusing the coated beads as a filler in thermoplastics, the proportion ofcoated beads is preferably from 30 to 40% by weight.

Composites according to the invention can be used in the manufacture ofa wide variety of articles, for example, articles of houseware, machineand structural components and decorative and/or functional fittings. Aspecific example of articles in the latter category is an instrumentpanel such as for a vehicle.

The invention includes coated glass beads suitable for use as asynthetic polymer filler, said beads being characterised in that thebeads bear surface coatings of synthetic polymeric material of which theglass transition temperature (T_(g)), determined by differentialscanning calorimetry, is lower than 15° C.

The coated bead may and preferably do have any of the optional featureshereinbefore referred to in relation to coated beads incorporated asfiller into a composite according to the invention.

The following are examples of coated beads and of composites accordingto the invention:

EXAMPLE 1

A filler according to the present invention, for use in a syntheticpolymeric matrix material was prepared by coating a batch of solidspherical glass beads with a polymeric coating material.

The mean diameter of the glass beads (i.e. the diameter which is suchthat half of the beads were above and half of them were below such mean)was 26μm. 90% of the beads had a diameter below 58μm and 10% had adiameter below 11μm.

The beads were immersed in a latex, i.e., in an aqueous solutioncomprising a styrene-butadiene copolymer (T_(g) of the butadiene units:below 15° C.) and a coupling agent comprising phenylsilane andaminosilane.

The beads wetted with such a latex were subsequently dried. The amountof copolymer forming the bead coatings was 1 g per kg of beads of whichthe specific surface was 0.3 m² /cm³. Such coatings have a negligible orvery low adherence to epoxy resin and low adherence to the glass beads.

The foregoing coated beads according to the invention were then mixed ina weight ratio of 1:1 with a matrix composition comprising an epoxyresin designated 818 marketed by Shell International together with apolyamine hardener marketed under the Trade Mark VERSAMID 140 by GeneralMills Co. and the resulting mixture was formed by extrusion into anarticle according to the present invention, the article being in theform of a sheet 3 mm in thickness.

A disc of this sheet material having a diameter of 3 cm was subjected toASTM Impact Resistance Test D 2794. The 9 impact resistance of thecomposite was found to be 2.00 kg.cm/mm.

For purposes of comparison, a composite having the same compositionexcept that the beads were not coated with the styrene-butadienecopolymer was formed into a sheet of the same thickness as the one abovereferred to and a sample of this further sheet material having the samedimensions as the above tested sample, was subjected to the same ASTDtest. This sample was found to have an impact resistance of only 1.35kg.cm/mm. A disc of the same size was formed from the copolymer alone,without filler, was also subjected to the same test. It has an impactresistance of about 2 kg.cm/mm.

EXAMPLE 2

A synthetic polymer filler according to the invention was prepared bycoating a batch of solid spherical glass beads having a mean diameter of46.5 μm, 90% of the beads being below 73 μm and 10% of them being below28 μm in diameter. The beads were treated with coupling agent and coatedwith styrene-butadiene copolymer in the same way as the glass beads inExample 1.

The beads were used as filler in preparing a mouldable composite. Thecomposite was prepared in the same way as in Example 1, using the samematrix material as in that Example, but the coated beads were used in aproportion of 33% by weight of the matrix material. Using the testreferred to in Example 1, the impact resistance of the composite wasfound to be 1.77 kg.cm/mm. The impact resistance of a composite of thesame composition except that the beads were uncoated was found to be1.25 kg.cm/mm.

EXAMPLE 3

A filler according to the invention was prepared as in Example 1, butusing a batch of solid spherical glass beads having a mean diameter of66 μm, 90% of the beads being below 103 μm and 10% of them being below42 μm in diameter. The beads were treated with coupling agent and coatedwith styrene-butadiene copolymer in the same way as the beads in Example1.

The beads were used as a filler in preparing a mouldable composite. Thecomposite was prepared in the same way as in Example 1, using the samematrix and the same coated bead/matrix ratio. The impact resistance ofthe composite was again found to be improved by the presence of the beadcoatings.

EXAMPLE 4

Coated beads identical with those used as the filler in Example 1 wereused as the filler in a composite comprising Nylon 6/6 marketed underthe Trade Mark MARANYL by Imperial Chemical Industries Limited. The beadcoatings have an adherence to polyamides which is very low. The beadswere used in a proportion of 15% by weight of the matrix material. Thecoated beads were mixed with the nylon powder within the screw of anextruder from which the composite was extruded as a rod. The rod wasthen cut into pieces which were supplied to an injection mouldingapparatus for forming into moulded articles.

The impact resistance of such moulded articles, determined by the testused in Example 1, was 4.67 kg.cm/mm. Articles formed in the same wayfrom a composite without the head coatings, but otherwise identical, hadan impact resistance of 3.67 kg.cm/mm.

Instead of mixing the coated beads and nylon within an extruder, theycan be mixed in some other mixing appliance and the mixture can then bedirectly injection moulded. However, this is not so suitable a procedurefor industrial scale operations.

An impact resistance better than that realised by the bead coatings inExample 4 was obtained when using an aliphatic polyurethane latexcontaining at least 10% of plasticiser for forming the bead coatingslimiting adherence to the nylon instead of the styrene-butadiene polymerlatex.

EXAMPLE 5

Various batches of glass beads having the granulometry set forth inExample 1 were mixed with nylon 6/6 powder in amounts of 30% by weightof the nylon and were moulded into plates 3 mm thick. The plates asmoulded were then subjected to the Gardner notched impact test withoutaging. One batch of beads was left untreated prior to its incorporationinto the synthetic polymeric material as a control, one batch wastreated with a known efficacious adhesion promoting agent forcomparison, namely amino-silane, and three further batches were treatedwith adhesion limiting agents in accordance with the invention. Theseagents were phenyl-silane, methyl-silane and an anionic fluorocarboncompound available from 3M Company under their designation FC 129. Thislatter material is a fluoro-alkyl-sulphonate of potassium. In each casein which the beads were coated, the coating was formed by mixing thebeads with a solution of the coating agent and then drying the beads toleave coating deposits of the amounts indicated in grams of the coatingagent per kilogram of the beads. The results are shown in Table I.

                  TABLE I                                                         ______________________________________                                        Bead coating agent                                                                         Quantity  Impact Resistance (Gardner)                            ______________________________________                                        Uncoated beads*                                                                            0.00 g/kg 9.4 kJ/m.sup.2                                         Amino-silane*                                                                              1.20      7.45                                                   Phenyl-silane                                                                              0.80      10.6                                                   Methyl-silane                                                                              0.80      10.3                                                   FC 129       0.80      10.8                                                   ______________________________________                                         * = Not according to the invention.                                      

Other samples of the same composition were extruded as pellets and theninjection moulded into plates which were then subjected to the Charpynotched impact resistance test, in the as-moulded (unaged) and in theaged condition. Aging was effected by storing the samples at 23° C. at50% relative humidity until equilibrium was reached. The results areshown in the following Table II.

                  TABLE II                                                        ______________________________________                                                        Impact Resistance                                                             kJ/m.sup.2 (Charpy)                                           Bead coating agent                                                                              Unaged   Aged                                               ______________________________________                                        Uncoated beads*   3.6      6.4                                                Amino-silane*     3.1      5.2                                                Phenyl-silane     5.0      8.3                                                Methyl-silane     5.2      8.4                                                FC 129            5.4      8.2                                                Unfilled nylon*   9 to 13  35 to 45                                           ______________________________________                                          *Not according to the invention.                                        

It was also found that when the amount of FC 129 fluorocarbon compoundwas reduced to 0.20 g/kg of the beads, similar results were still given.

I claim:
 1. A polymeric article comprising a synthetic polymer matrixand a filler material, the synthetic polymer matrix being comprised of asynthetic polymer selected from the group consisting of polyamides,polystyrene, epoxy resins, and polyester resins, and the filler materialbeing comprised of glass beads bearing at least one coating in a totalcoating amount ranging from 0.02 up to 1% by weight based on the weightof uncoated glass beads, which at least one coating comprises at leastone coating agent comprising at least one silicon-functional silaneselected from the group consisting of alkyl-silanes and aryl silanes andwhich at least one coating limits adhesion between the glass beads andthe synthetic polymer matrix, and confers an increased impact resistanceon the article as compared with an article which includes uncoated glassbeads as filler material but is otherwise identical.
 2. The polymericarticle according to claim 1, wherein said coating amount ranges from0.02% up to 0.2% by weight based on the weight of the uncoated glassbeads.
 3. The polymeric article according to claim 1, wherein saidcoating amount is not more than 0.1% by weight based on the weight ofthe uncoated glass beads.
 4. The polymeric article according to claim 1,wherein said at least one silicon-functional silane is one of amethyl-silane and a phenyl-silane.
 5. The polymeric article according toclaim 1, wherein the glass beads are solid.
 6. The polymeric articleaccording to claim 1, wherein the glass beads are spherical.
 7. Thepolymeric article according to claim 1, wherein the diameters of theglass beads are below 200 μm.
 8. The polymeric article according toclaim 1, wherein the glass beads have an apparent bulk density of from1.5 to 1.55.
 9. The polymeric article according to claim 1, wherein thegranulometry of the glass beads is such that 90% of the beads have adiameter smaller than a length x and 10% of the beads have a diametersmaller than a length y, the values of x and y being such that x - y isgreater than 45 μm but smaller than 65 μm.
 10. The polymeric articleaccording to claim 1, further comprising a finely divided material whichis included in the filler material and modifies the bulk densitythereof.
 11. The polymeric article according to claim 10, wherein saidfinely divided material is a hydrophobic, inorganic substance which issubstantially chemically inert with respect to the glass beads and has aspecific surface of at least 50m² /g.
 12. The polymeric articleaccording to claim 1, wherein said at least one silicon-functionalsilane comprises a mixture of two different silicon-functional silanesand forms an interfacial bond of a strength intermediate that attainableby either of two such silanes if used alone, respectively.
 13. Thepolymeric article according to claim 1, wherein the at least one coatingagent comprises a silicon-functional silane and a silane, thesilicon-functional silane and the silane forming a mixture of silanes,which mixture forms an interfacial bond of a strength intermediate thatattainable by either of two such silanes if used alone, respectively.14. Coated glass beads suitable for use as a filler material forsynthetic polymers, said coated glass beads comprising glass beadshaving at least one coating comprised of at least one coating agent,which at least one coating agent comprises at least onesilicon-functional silane selected from the group consisting ofalkyl-silanes and aryl silanes, and said coated glass beads having atotal coating amount ranging from 0.02 up to 1% by weight based on theweight of uncoated glass beads.